Caldera volcanoes are the Extreme Volcanoes. These are the most powerful and catastrophic types of volcanoes in a category by themselves because of the unique way in which they form. This type of volcano is shaped more like an inverse volcano. An enormous magma chamber bulges up beneath the ground from the extremely high pressures of the trapped gases within. Ring-shaped cracks form outward from the magma chamber toward the surface and these act as relief valves for the magma to escape. Once the accumulated pressure has been sufficiently released through a serious of extremely powerful pyroclastic and plinian eruptions, the ground above the magma chamber subsides or caves in, leaving a large depression. Caldera volcanoes are the largest on earth, with some calderas measuring from 15 to 100 kilometers wide.

Scientists are just beginning to understand these types of volcanoes and have only recently identified the characteristics of this type of eruption. Since this type of eruption has not occurred anytime during recorded history there have been no human witnesses to record observations of this type of event. The lack of a real-world example makes it even more difficult for scientists to study this type of volcano and very little about them is understood. But from the evidence that scientists have been able to gather about caldera eruptions in earth's past, all signs point to events so cataclysmic that they may have changed the course of the evolution of life on earth. Witness the following eruptions:

Toba Eruption
Approximately 74,000 years ago on the island of Sumatra, Indonesia, a volcanic eruption so violent occurred that it proved to be apocalyptic for the human race. Scientists estimate that the eruption may have ejected up to 6,000 km3 of magma and pulverized rock and sufficient sulfur gases to form 5,000 megatons of stratospheric sulfuric acid aerosols. The suspension of so much material in the earth's atmosphere resulted in a volcanic winter that lasted all year long, every year for several years. The severe drop in global temperatures had catastrophic effects on vegetation and the food chain dependent upon it for survival - including humans.

Scientists have examined the genetic codes of seemingly disparate and distant races of people and found there's actually very little genetic variability in the entire human race. The evidence indicates that something happened to the human gene pool approximately 74,000 years ago where only a very few humans remained alive on the planet (say 5,000 to 10,000), and the current population has grown from these selectively few genotypes. Our existence in such great numbers today (over 6 billion strong) is a testament to our tenacious ability to survive. But could an eruption like that happen again? Some scientists are studying the evidence and believe that there's a real possibility it could happen in the Yellowstone Caldera…

The Yellowstone Caldera Yellowstone National Park in Wyoming, USA is a haven for vacationers and tourists coming to appreciate the area's rugged natural beauty. It is also an attraction because of its mysterious volcanic activity. In the last 50 years scientists have been closely studying the volcanic activity in the Yellowstone area to understand the source of this smoldering cauldron and how it has behaved in the past. By studying the pattern of eruptions in the past, scientists hope to predict what it will do in the future.

Scientists estimate that approximately 2.1 million years ago the first large caldera-forming eruption occurred in the Yellowstone area. From the evidence they have gathered it appears there have been three such cataclysmic eruptions in the Yellowstone area in the last 2.1 million years, each occurring at intervals of 600,00 to 800,00 years apart. The most recent eruption in the Yellowstone Caldera occurred 640,000 years ago. The 2.1 million year old eruptions represent the greatest volcanice eruptions on earth.

According to the U.S. Geological Survey…The three caldera-forming eruptions, respectively, were about 2,500, 280, and 1,000 times larger than the May 18, 1980 eruption of Mt. St. Helens in Washington State. Together, the three catastrophic eruptions expelled enough ash and lava to fill the Grand Canyon."

The initial eruption of 2.1 million years ago was 2,500 times more powerful than the Mt. St. Helens eruption and perhaps was the largest, most violent volcanic eruption in the history of earth. Enough ash and volcanic debris exploded from the eruptions to cover the entire western half of the United States with about a four-foot deep layer of ash. Roughly 600 cubic miles of material were thrown into the atmosphere. Unlike many of the world's caldera-forming volcanoes that are found over subducting tectonic plates, the Yellowstone Caldera is fed by what geologists call a hot spot beneath the crust. This is the theory that explains how volcanic activity can occur in the middle of tectonic plates, away from geologically active plate margins.

An enormous magma chamber 40 by 80 kilometers lies in wait beneath the giant Yellowstone Caldera. Scientists have recently surveyed the ground in the enormous caldera and have found the ground seems to be bulging upward, indicating the magma chamber is on the move. Since there are no historical precedents for this type of eruption, scientists do not know how to predict if a giant caldera-forming eruption will occur again. One thing they do know is that the Yellowstone eruptions were far, far more powerful and violent than the Toba eruption of 74,000 years ago. If the Toba eruption could reduce the human species to a few scrappy survivors, can you imagine what another eruption of the Yellowstone Caldera could do to us?